[doc] Fix example about Community view customization

[doc] Add command pip install of new cube

[doc] update cubicweb version

[doc, blog tutorial] Remove cubicweb-dev from pip dependencies This pip package does not exist

[doc] Add requirement for gettext and graphviz When running the tutorial from scratch, I had errors because these two packages were not installed.

Added tag 3.27.3, debian/3.27.3-1 for changeset 85284f028266

[pkg] version 3.27.3

[pkg] require python >= 3.6 in debian packaging

[pkg] merge 3.27 Require python >= 3.6 since recent typing notations require >= 3.6

[pkg] add python3 only pypi specifiers This is only for pypi statistics purposes. Also add 'Programming Language :: Python', looks obvious but seems to be sane to have this as well.

[pkg] the wheel is no longer universal Since we're only py3 compatible. In practice this changes nothing since we don't upload cubicweb wheels to pypi.

[pkg] require python >= 3.4 This avoid pip pulling a version that does not run on python2 when using a python2 environment. Since we already released some 3.27 releases in pypi, I think we should release 3.27.3 and remove releases 3.27.2, 3.27.1 and 3.27.0 from pypi.